Cameron - that's weird that a standard 5.0 motor didn't fit under the scoop! When PCC gets back from the land of warm beer and cold women (
), he'll no doubt let you know if his engine fits OK.
GT40 heads won't mean a GT40 manifold. The GT40 manifold his individual tubular runners from the upper plenum down to the lower intake. The standard upper intake is a one-piece unit.